Even pressure piston



April 12,1938. M. A. BECKMANN V EVEN PRESSURE PISTON Filed May 12, 1956 2 Sheets-Sheet 1 lNVENTb R. I

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'- V A ORNE April 12, 1938.

M. A. BECKMANN EVEN PRESSURE PISTON Filed May 12, 1936 2 Sheets-Sheet 2 Patented Apr. 12, 1938 UNITED STATES PATENT OFFICE signor to Aluminum Industries, Incorporated,

Cincinnati, Ohio, a corporation of Ohio Application May 12,

Claims.

This invention relates to a piston for internal combustion engines especially those of automobiles, and is especially adapted for those made from aluminum alloys. Other metals may be 5 used however.

The general object of the invention is to provide a piston that will bear evenly on the cylinder wall at substantially all points of the piston's surface and at substantially all times and temperatures.

Another'object is to provide a construction in which the flow of heat from one part of the piston to another is unhampered altho a slot in the skirt is provided, which ordinarily would be a bar 'to heat flow.

Another object is to provide a piston in which the skirt is reinforced against collapse in such a way that the reinforcement has the greatest strength where it is the most needed. Conversely, the greatest amount of diameter adjustment is obtained where it is most necessary.

Another object is to provide a piston which is stabilized against rocking.

Briefly stated, the invention resides in the combination'of a cam ground slotted skirt piston with a hairpin or segment-enclosing bridge or gusset across the slot, the bridge being integral with the piston body. The height of the hairpin bridge increases progressively toward the bottom of the skirt so as to obtain a gusset function of progressive rigidity, increasing toward the piston head.

Last but not least, an object of the invention is to provide these advantages in a form that will be commercially successful because it is well adapted to production by the permanent mold process.

Heretofore it has been attempted to reinforce the skirts of slotted pistons with steel springs of various shapes, commonly called expanders. These press the skirt against the cylinder wall when the piston is cold, making starting diificult and when the piston becomes hot they do not promote even heat'distribution in an aluminum piston because their heat conductivity is so much less than that of aluminum. My reinforcement has no spring action nor does it diminish heat flow, yet it strengthens the skirt and holds it in proper working position. 'Because the skirt is so held, the p ston has less tendency to rock.

In the drawings, Fig. 1 is an elevation, partly in section, of my piston, the sectional part being taken along the vertical part of the slot.

Fig. 2 is a plan view of the piston with portions of the piston head broken away and the bridge and pin bosses shown in dotted line. The cam 1936, Serial No. 79,309

grinding of the piston is exaggerated for purposes of illustration.

Fig. 3 is a transverse sectional view taken along the line 3-3 of Fig. 1.

Fig. 4 is an elevation of that side of the piston on which the slot and bridge are located.

As shown, i0 is the hollow head, H the skirt of the piston and I2 the usual ring grooves. Below the grooves. 90 away from the pin bosses l3 there is a T-slot comprising a short horizontal slot I4 g and a relatively longer, slightly slanted, almost vertical slot l5. The pin bosses have the usual. hole l8. Straddling the slot l5 there isa hairpin bridge I6 which extends vertically from a point just under the head Hi to a distance of /4" to from the bottom of the skirt on an ordinary passenger automobile piston. At the top, the bridge is considerably narrower than at the bottom, altho its angle of dehiscence remains the same. This implies that the back ridge ll of the bridge is not vertical and in fact, it slants toward the lower part of the vertical middle axis of the piston. The bridge is cast integrally with thepston. It is cut by the slot M which severs the upper tip from the skirt portion. The upper tip 2 is solid.

By the hairpin bridge I mean a bridge having a cross-section shapedlike the connecting portion between the two arms of a conventional hairpin.

The angle of dehiscence of the bridge from its ridge to the skirt is preferably 15 degrees ncluded angle) but may range from 10 to When a 15 angle is employed, the piston is camground as shown in Figs. 2 and 3. the diameter thru the pin bosses is from three to ten thousandths of an inch shorter than the diameter at degrees to said p n boss. This gr nd ing is employed because the piston has a greater expansion along the pin bosses than in a direction 90 from them. No originality is claimed for cam-grinding per se', but in combination with the bridge. even pressure on the cylinder walls is produ ed over the entire piston. which is not the case with a cam-ground piston that lacks my bridge. On the other hand my bridge on a round p ston produces a result that in certain cases eliminates the need for a cam-grinding to obtain substantially e en pressure. Such construction is disclosed in my co-pending application Serial No. 79,310 filed May 12, 1936. Nevertheless, 'it lies within the scope of the present invention to employ the bridge of increasing height herein disclosed on a round piston because a round piston even with no special features except the bridge 4 That is to say, 1

and slot, will give better results than any round piston without them or with only a slot.

In operation the superior efi'ects occur as will now be described in the case of the construction shown, applied to an automobile piston 3 /2" diameter by 4" long. This piston is cam-ground to six thousandths diameter differential and has a This alloy has a coeflicient of expansion of 0.000011 inch per inch per degree Fahrenheit up to 500 Fahrenheit.

As the engine heats, the piston expands on both diametrical axes simultaneously and reaches even pressure in both directions simultaneously. The bridge has no tendency to push the skirt against the cylinder wall as occurs in the case of steel expanders, since the bridge is made of the same metal as the skirt. A steel spring expander makes an engine hard to start and this is not the case with my bridge because it does not act as a spring, but as a gusset. Some steel expanders interrupt heat flow. The function of my bridge is to stabilize the piston and to keep the skirt from collapsing. In an automobile engine, the greatest pressure on the piston is exerted on that side which is on the right from the driver's seat. That is the side here shown uncut vertically and experience has shown that it is the side which should so remain. The opposite side therefore is the one which should have the function of adjusting itself to the cylinder and this is the one selected for my bridge.

As is well known, the head of a'piston is the end which grows hottest in use. Since the skirt does not grow so hot, it is necessary to have smaller clearances at the bottom of the skirt when the piston is put into service, than would be necessary if the piston attained the same heat all the way down. In the present invention, close attention need be paid only to head clearances because the skirt will adjust itself. This is because the bridge 16 is progressively higher at the bottom of the skirt than at the top. Consequently, the skirt can be more easily compressed at the bottom while at the top it is held with greater rigidity against heat expansion. 1

The net result is that a piston built according to this invention adapts itself according to its temperature to bear on the cylinder walls with substantially equal pressure top and bottom, left and right. The bridge limits the "accordion action of the split skirt, thereby avoiding metal fatigue due to long repeated bending during operation.

At the same time, a close enough fit of the skirt in the cylinder is maintained so that the piston has little or no tendency to rockend for end. This is what'I call stabilizing action. The clearance is always substantially the same, hot or cold in a diametrical direction across the piston pin axis. When the piston heats in operation, the diameter along the piston pin axis becomes the same as the diameter across it. So the piston is entirely round when hot due to practically complete closing of slot l5 but both stabilized and reinforced whether hot or cold.

It is of course, necessary to adopt different clearances in cam-grinding when an alloy of a different coeflicient of expansion is used than the one mentioned. This is however, a matter that any competent piston designer can solve if he is acquainted with the principles herein disclosed. The operating temperatures in the engine also have some eifect but the principles are operative up to the incipient fusing points of the metals employed.

In the construction here shown it is easy to pull out the iron core used in the permanent mold to make the hairpin bridge hollow. This is because of ample draft since the bottom of the core is smaller than the top. The facility of producing the entire piston by the permanent mold process is shown in my co-pending application Serial No. 85,946, filed June 18, 1936. No machining of the bridge is required.

I claim as my invention:-

1. A piston for internal combustion engines which comprises a head, a skirt attached thereto, piston pin bosses within said skirt, a T slot in said skirt at substantially 90 from the axis of said bosses and an integral hairpin bridge adapted to act as a gusset, said bridge joining the ends of the skirt across said slot, the height of said bridge increasing progressively toward the bottom of the skirt.

2. A piston for internal combustion engines which comprises a head, a skirt attached thereto, a pair of piston pin bosses within said skirt, a T slot in said skirt at substantially 90 from the axis of said bosses, an integral hairpin bridge adapted to act as a gusset, said bridge joining the ends of the skirt across said slot having an angle of dehiscence of about 15 and increasing in height toward the bottom of the skirt.

3. A piston for internal combustion engines which comprises a head, a skirt attached thereto and a pair of pin bosses within the skirt; said piston being from 3 to thousandths of an inch shorter across that diameter which coincides with the piston pin boss axis than that diameter which lies at 90 therefrom, a-T slot in said skirt 90 from the axis of said bosses and an integral hairpin bridge joining the ends of said skirt across said slot the height of said bridge increasing toward the bottom of the skirt.

4. A piston for internal combustion engines which comprises a head, a skirt attached thereto and a pair of pin bosses within the skirt, said piston being from 3 to 10 thousandths of an inch shorter across that diameter which coincides with the piston pin boss axis than that diameter which lies at 90 therefrom, a T slot in said skirt 90 from the axis of said bosses and an integral hairpin bridge joining the ends of said skirt across said slot the height of said bridge increasing toward the bottom of the skirt, the metal of the piston having a coefficient of expansion of substantially 0.000011 inch per inch per degree Fahrenheit.

5. A piston for internal combustion engines which comprises a head, a skirt attached thereto, piston pin bosses in said skirt, a T-slot in said skirt at substantially 90 from the axis of said bosses and an integral bridge acting as a gusset and joining the ends of a skirt across said slot, said bridge comprising relatively thin and relatively high walls converging at a dihedral angle in the vicinity of to a rounded connecting portion, and said bridge increasing in height toward the bottom of the skirt.

MELBOURNE A. BECKMANN. 

